It is myth that the use of short musical sequences, of say under 20 seconds, is exempt from copyright regulations.
It is a basic tenet of copyright law worldwide that only a copyright owner has the right to copy or reproduce their original work. Any other person who copies or reproduces, or appropriates another's copyright work will be acting in breach of copyright law, and will be required to provide financial compensation for having done so without prior authorization.
A minority of samplers / appropriators / infringers are pursued by the copyright owners of an original sound or film recording, usually when the sampled / appropriated work has achieved a significant degree of commercial success and its commercial value needs to be protected. An example of this was the action taken in the Supreme Court of Justice in the U.S. against the hip-hop band 2 Live Crew, who had sampled / appropriated the first five notes from the original sound recording of Roy Orbison's ‘Pretty Woman’. This amounted to less than four seconds or barely one bar of music. The band had looped the sample and used it to create their own sound recorded version of Pretty Woman, using their own version of the original lyrics. The U.S. Supreme Court however had no hesitation in finding that this deliberate sampling was a palpable breach of copyright.
You should always consider writing to the copyright owner for their permission to use music or any other copyright protected material, briefly explaining the appropriateness of it to your work, how the work will be shown / seen and where, and most importantly whether there will be a commercial dimension involved in the performance based work, i.e. will it generate income for you. If it's a non-commercial project, the chances are good that permission will be given without requiring payment, but with an acknowledgement being given. Conversely, if it is a commercial project then the record company is likely to want a fee/income share for the licence.
For information on an artist project working with music where copyright protection has expired, watch our film of Ben White and Eileen Simpson's Open Music Archive, part of our ArtlawTV series.